Ribot studied law and rose to be director of the Department of Criminal Affairs at the Ministry of Justice. He was elected in 1878 to represent Pas-de-Calais in the Chamber of Deputies. Ribot was a moderate republican, and he specialized in financial matters. He lost his seat in October 1885 but was returned for Pas-de-Calais in 1887 and thereafter held the post until his election to the Senate in 1909. As minister of foreign affairs from March 1890 to February 1892, he initiated the rapprochement with Russia that was to ripen into alliance in 1894. He resumed the portfolio of foreign affairs when he became premier on Dec. 6, 1892, but his government fell four months later in the Panama Canal scandal. Premier again and also minister of finance from Jan. 26, 1895, Ribot sponsored the expedition to establish a protectorate over Madagascar, but he once again was forced to resign over a financial scandal.

Ribot was in the opposition from 1896 to 1914. He became a member of the Académie Française in 1906. In 1909 he was elected senator for Pas-de-Calais; in this role he specialized in foreign policy. In June 1914, he served very briefly as premier. After this government fell, he was appointed minister of justice; and in August of that year, after the outbreak of World War I, he again became minister of finance. He held this post for more than 2 years. He was again premier and minister of foreign affairs in March–September 1917, his most important act being to make General Philippe Pétain commander in chief of the French armies in May of that year.